BCECE Engineering BCECE Engineering Solved Paper-2003

  • question_answer
    An observer moves towards a stationary source of sound with a velocity one-tenth the velocity of sound. The apparent increase in frequency is:

    A)  zero                                     

    B)         10%

    C)         5%                                        

    D)         0.1%

    Correct Answer: B

    Solution :

    Key Idea: The perceived frequency of source depends on the relative motion between the source and the observer. The perceived frequency of source observed by the observer is given by \[n=n\left( \frac{v\pm {{v}_{o}}}{v\pm {{v}_{s}}} \right)\] As sound source is stationary and observer is moving toward the source, we conclude                 \[n=n\left( \frac{v+{{v}_{o}}}{v} \right)\]              \[(\because \,{{v}_{s}}=0)\]                 Given,                   \[{{v}_{o}}=\frac{v}{10}\]                 \[\therefore \]  \[n=n\left( \frac{v+v/10}{v} \right)\]                 or            \[\frac{n}{n}=\frac{11}{10}\] Hence, apparent increase in frequency is given by \[\frac{n-n}{n}=\frac{11-10}{10}=0.1=10%\]


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